From document U.S. Pat. No. 5,135,539, a heart prosthesis being implantable in the pericardial cavity of a patient is known, said prosthesis being capable of replacing the natural left and right ventricles of said patient after ablation thereof and comprising:                a stiff body in which artificial left and right ventricles are arranged, each of these artificial ventricles comprising a soft pulsatile membrane:                    which is capable of beating under the action of a hydraulic fluid, and            which is provided within a cavity sealingly partitioned by said membrane into two chambers, one of which is intended for blood flow and the other of which is intended for said hydraulic fluid, the blood chamber of the artificial left ventricle being intended to be connected to the natural left atrium and to the aorta, whereas the blood chamber of the artificial right ventricle is intended to be connected to the natural right atrium and to the pulmonary artery;                        two hydraulic actuators connected to the hydraulic fluid chambers of said cavities within said stiff body, for alternately injecting therein and expulsing therefrom hydraulic fluid and providing desired values of diastolic and systolic flow rates; and        a soft bag widely and sealingly surrounding at least one portion of said stiff body while enclosing said hydraulic actuators, said soft bag serving both as a hydraulic fluid reservoir for said hydraulic actuators and as a compliance chamber.        
In this known heart prosthesis, each actuator is associated with a ventricle and, in order to comply with physiology, both actuators can operate independently from each other and particularly in a synchronised way, that is both ventricles can be respectively and simultaneously either in diastole or in systole. In this case, the result is that said soft bag undergoes large displacements, since the whole fluid required for animating right and left pulsatile membranes is alternately injected, and then drawn into said soft bag. If the capacity of each ventricle is of about 75 cm3, the volume variations of the bag may reach 150 cm3. Such high amplitude beats of the bag, on the one hand, may raise issues of housing said prosthesis within the pericardial cavity and, on the other hand, cause an inflammation of the surrounding tissue, with the risk for a thick fibrous capsule to occur, capable of hindering the beats of the bag and altering the operation of the prosthesis.
Besides, such a synchronised operation requires that both actuators are capable of the same performance, which is of a high power cost.
In order to overcome these drawbacks, it could be possible, as suggested by document WO-0,191,828, to remove one of said actuators and operate the ventricles in phase opposition, one of said ventricles being in diastole whereas the other is in systole. Thus, the hydraulic fluid is transferred from a ventricle into the other with much reduced beats of the bag. In addition, such a heart prosthesis is advantageous in terms of space and power consumption, since it only comprises one actuator. However, it has the drawback of controlling the intake duration of one of the ventricles based on the ejection of the other, such that the diastole durations are necessarily equal to the systole durations, which does not enable physiology to be complied with. In addition, such a heart prosthesis with one single actuator has the risk, in operation, of either drawing the atria and failing to fill the ventricles, or performing too slow ejection and not maintaining a proper pressure.